my system is tank fed by central heating boiler with diverter.
i have had endless problems with my central heating and hot water.
basically we have switched the central heating on and all the radiators
eventually all worked after bleeding riser pipe next to tank.but again
we can only fill the bath about a quarter before it goes cold.
before we switched heating on there was plenty.

this is the same problem as last winter. also the radiators arent fully
hot.
things we have had done;-

new diverter valve,new thermostat, a sludge remover put into heating
system along with an inhibitor
the pump was changed about 4 years ago.
any ideas? could it be the pump again?